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Prognostic factors in dogs with head trauma | VETgirl Veterinary CE Podcasts

In today’s VETgirl online veterinary continuing education podcast,  we review prognostic factors in dogs with head trauma based off a recent study by Sharma et al entitled Retrospective evaluation of prognostic indicators in dogs with head trauma.” Many of us in emergency practice see head trauma patients and would agree that the prognosis for these patients can be difficult to predict.  Some dogs or cats admitted with signs of traumatic brain injury make astounding turnarounds, whereas others do not seem to respond to therapy.  Studies investigating veterinary patients with head trauma are relatively sparse.  A study investigating the utility of a modified Glasgow coma scale score (MGCS) was published back in 2001 and showed an almost linear correlation between the score and mortality.  Alternatively, large studies investigating the utility of the Animal Trauma Triage (ATT) score have been published recently, but this score has not been specifically investigated in a population of head trauma patients.  Therefore, the purpose of this study was to determine whether clinical and laboratory variables or scoring systems such as the modified Glasgow coma scale, mentation, or ATT scores recorded at hospital admission have prognostic value in dogs with head trauma.

This was a retrospective study that evaluated dogs sustaining head trauma within 5 days of admission to the Ontario Veterinary College between January 2001 and March 2011. Dogs were excluded if they had pre-existing neurologic disease, an inconclusive history of trauma, or missing medical record information.  Information from the first 6 hours of admission was included and the closest values to admission chosen if multiple measurements were taken.  Signalment, history, treatments performed at the referring clinic, and several clinical and laboratory variables were recorded such as vital signs and blood gases. Findings from the neurologic assessment and physical exam were used to calculate the MGCS, mentation, and ATT scores. Other recorded information included the use of interventions such as mannitol or hypertonic saline, oxygen supplementation, or endotracheal intubation, as well as benzodiazepine, anti-seizure medication, or steroid administration. Outcome was recorded as survival or non-survival to hospital discharge.

Overall, 72 dogs were included in the study (with an average age of 2). 89% of the dogs sustained blunt head trauma, more than half of which were due to motor vehicle accidents. The overall mortality was 15%, with 91% of non-surviving dogs being euthanized. Of the 72 dogs, 89% had neurologic deficits suggesting traumatic brain injury, as indicated by a MGCS score less than 18, which is normal. Of the clinical and laboratory values recorded, lower SpO2, pH, bicarbonate, base excess, total protein, and albumin, as well as higher potassium, lactate, or BUN were predictors of non-survival.

All 3 scoring systems were also predictive of non-survival, although ROC curve analysis revealed that the MGCS had the highest predictive value. Remember that the MGCS is calculated based on 3 categories, each assigned a score of 1-6 points; the lower the score, the more severe the brain injury. (VETgirl is very geeky and has a living will specifically stating that if my GCS is < than a certain number, turn off the vent, baby! BTW, this is your public service announcement for you to fill out a living will for your loved ones and yourself right now. No, seriously.) Anyway, back to the MGCS, the categories are motor activity, brainstem reflexes, and level of consciousness. In this study, an MGCS score > 15 predicted 100% survival. However, a score of 7 resulted in a 54% probability of non-survival. A  MGCS ≤ 11 was 84% sensitive and 73% specific when it came to predicting non-survival.

For comparison, the ATT score was first described in 1994 and is calculated based on 6 categories, each assigned a score of 0-3.  The categories are perfusion, cardiac, respiratory, skeletal, neurological, and eye/muscle/integument (all in 1 category) with the higher the score, the more severe the injuries sustained.  A 51% probability of survival was found at an ATT score of 9.

Finally, a mentation score, which is part of the APPLE score that was first described in 2010, is calculated using a score of 0-4 with 0 being normal and 4 being unable to stand and unresponsive.  A mentation score of less than or equal to 2, which is dull mentation and can stand only when assisted, was predictive of 100% survival.

In terms of treatment variables, dogs that were given hypertonic saline were 5 times less likely to survive and dogs that were endotracheally intubated were 10 times less likely to survive.  Additionally, dogs that received mannitol or oxygen therapy had lower MGCS and higher mentation scores, both indicative of worse traumatic brain injury.

So…what is the importance of these findings and worth discussing in more detail?  It’s interesting to note that laboratory findings indicative of poor perfusion and oxygenation were predictive of non-survival. Specifically, lower pH, bicarbonate, and base excess and higher lactate, potassium, and BUN all indicate hypoperfusion. The presence of systemic hypoperfusion suggests that cerebral hypoperfusion or ischemia also occurred, which is known to exacerbate secondary brain injury by promoting free radical production and cerebral edema. Interestingly, low blood pressure was not statistically associated with non-survival in these dogs; however, some of the non-surviving dogs did not have blood pressures recorded, so the study was likely underpowered to detect this. This doesn’t mean that you can blow of blood pressure. Maintenance of adequate blood pressure is imperative to successfully manage patients with traumatic brain injury. This is based on the formula for cerebral perfusion pressure, which is determined by the mean arterial pressure minus the intracranial pressure. Therefore, when intracranial pressure increases in patients with traumatic brain injury, the mean arterial pressure must also increase to maintain cerebral perfusion. As such, we typically aim for a mean arterial pressure of 80-90 mmHg, rather than our traditional 65-75 mmHg during resuscitation of head trauma patients, in order to preserve adequate blood flow to the brain. Likewise, a lower SpO2, which indicates hypoxia, is also a known risk factor for worsening secondary brain injury in people, so efforts should be made to ensure adequate oxygen delivery by using oxygen supplementation to normalize SpO2 in patients with traumatic brain injury.

Also, as already mentioned, all of the investigated scoring systems were good predictors of outcome in this group of dogs.  Specifically, dogs with a lower likelihood of survival had lower MGCS, higher ATT scores, and higher mentation scores. Practically speaking, about a 50% chance of survival can be given for dogs with an MGCS score of 7 or an ATT score of 9; whereas, all dogs with a mentation score of 2 or less survived. While many clinicians like to use these scoring systems to monitor patients and assign a more objective assessment that can be compared to serial assessments, especially those made by other clinicians, these scores should not be used alone to advise owners as to whether or not to continue treatment for their pet. As evidenced in this study, there is a wide range of overlap between the surviving and non-surviving dogs in that several dogs with worse scores and severe traumatic brain injury still survived (after all, dogs don’t need to read or write and we accept a lower cognitive function). Therefore, serial assessments should be made and several prognostic indicators taken into account when assisting owners in their decision-making.

Treatment modalities that were associated with non-survival in this study included the administration of hypertonic saline or endotracheal intubation. This is not surprising given that clinicians probably opted for these modalities in patients with severe traumatic brain injury. Hypertonic saline is the treatment of choice for human patients with elevated intracranial pressure, because it has intravascular volume expansive properties that improve mean arterial pressure and its hypertonicity helps to reduce intracranial pressure. Alternatively, endotracheal intubation is usually reserved for patients with an absent gag reflex that are unable to protect their airway, thus indicating severe brainstem injury. Likewise, patients might be intubated if they are hypoventilating, since hypercapnia ( a high pCO2) will lead to cerebral vasodilation and worsening intracranial pressure elevations. It is unlikely that these treatments caused non-survival in these dogs, but rather were associated with worsened brain injury, which led to death.

Although the administration of steroids was investigated for its prognostic value, this study was underpowered to detect a difference between survivors and non-survivors. However, given the astounding evidence against steroid use in human head trauma patients as revealed in the widely publicized CRASH trial, steroids are no longer recommended in veterinary patients. And while hyperglycemia at hospital admission has previously been associated with more severe head injury, this study did not show that blood glucose was predictive of outcome. However, given that some dogs did not present to this tertiary referral hospital until hours or even days after their head trauma, a true admission hyperglycemia might have been missed.

The limitations of this study should be stated, including its retrospective nature and variable time to hospital admission from the time of head injury. Prospective evaluation of prognostic indicators in a larger population of dogs is needed and will likely be achieved now that a large veterinary trauma database has been established in the USA.

So, with all that, what do we take from this VETgirl podcast? The take-home points of this study are to ensure that dogs coming to your hospital after head trauma are adequately resuscitated so that they have normal perfusion and also given oxygen supplementation if they have an SpO2 < 95%.  A MGCS score can also be used with serial measurements taken over time to provide more objective assessments of improvement and assist clinicians and owners in their decision making. Make sure you fully assess neurologic function before you administer any analgesics! Keep in mind that scoring systems are not fool-proof and should not be used alone when guiding owners…ultimately, there is still no substitute for patient assessments and clinical intuition!

References:

  1. Sharma D, Holowaychuk MK. Retrospective evaluation of prognostic indicators in dogs with head trauma: 72 cases (January 2001–March 2011). J Vet Emerg Crit Care 2015;25(5):631-639.

 

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